The Evolution and Developmental Expression Profile of the PIN-FORMED Family in Setaria viridis

Auxin is one of the major driving forces of plant development and requires careful regulation of transporter proteins to establish polar auxin transport. The PIN-FORMED (PIN) family plays a pivotal role in plant development by establishing auxin gradients that govern vascular patterning and organogenesis. However, the PIN family remains severely underexplored in Setaria viridis, a well-established model for C4 monocots. In this study, we identified and characterized 13 PIN genes in the S. viridis genome. Phylogenetic and collinearity analyses revealed duplication events in the SvPIN1, SvPIN5 and SvPIN10 subfamilies. Structural analysis uncovered unique features, including potential pseudogenization of SvPIN5a. Expression profiling across five developmental stages unveiled the potential developmental roles of SvPINs, with SvPIN1 and SvPIN10 paralogues predominantly expressed in shoots and panicles, SvPIN2 and SvPIN9 in roots, while SvPIN5b showed leaf-enriched expression, suggesting potential involvement in Kranz anatomy development. Hormonal treatments in callus cultures revealed auxin-mediated upregulation of SvPIN1b, SvPIN2, SvPIN5d, SvPIN8 and SvPIN10a. Our findings provide significant insights into the role of PIN genes in S. viridis and other C4 monocots, establishing a foundation for future functional studies and offering potential targets for crop improvement through auxin transport manipulation.